Powder coating composition employing mixture of polyepoxide resin with modified polyester resin

ABSTRACT

Thermosetting coating compositions for powder coating processes, having a good powder stability, comprise a mixture of 4-25 wt % of a polyepoxide resin, the average molecule of which contains at least two epoxy groups, and 75-96 wt % of a solid modified polyester resin having an acid number of 30-100 and softens in the range of 60° C.-130° C. The solid modified polyester resin is the reaction product of an anhydride of a polybasic, organic carboxylic acid and a polyester having a hydroxyl number of 15-50 derived from a dibasic aromatic carboxylic acid and a specific alcohol component.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 624,693 filedOct. 22, 1975 and now abandoned, which in turn is a continuation ofapplication Ser. No. 316,943 filed Dec. 20, 1972 and now abandoned,which in turn is a continuation-in-part of application Ser. No. 211,648filed Dec. 23, 1971 and now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to thermosetting coating compositions which aresuitable for application by powder spray methods and fluidized bedcoating processes, and methods for the production of such coatingcompositions. More particularly, this invention relates to solid,modified polyester resins which are cross-linked by polyepoxide resinsand to thermosetting coating compositions comprising said modifiedpolyester resins and polyepoxide resin cross-linking agent, whichcoating compositions are in the form of a stable free-flowing powder,suitable for application by powder spray methods and fluidized bedcoating processes.

2. The Prior Art

Generally, thermosetting curable coating compositions are in the form ofa solution of a synthetic resin in an organic solvent serving as acarrier. This solution is applied to the base surface, which may bemetal, wood, paper or textile, after which the solvent carrier isevaporated and a synthetic resin film remains, which then may besubjected to a heat-hardening treatment.

The use of organic solvents as a carrier for the synthetic resin has thedisadvantage that in most cases the solvents are inflammable or even maygive rise to explosions. Moreover some organic solvents arephysiologically unacceptable as they endanger the health of operators.In addition, much energy is required for the evaporation of the organicsolvent and for the conditioning of the air which must carry away thesolvent vapors from the oven in which the coated objects are baked.

For these reasons it has been proposed to replace the organic solventswholly or partially by water. The use of water as a carrier for thesynthetic resin, however, dictates the use of certain types of syntheticresins, which might not impart the required technological properties,such as flow, levelling and gloss to the finished coatings.

In view of the disadvantages of the preceding methods, it has also beenproposed to apply high-melting thermoplastic, non-curable coatingcompositions in the form of a homogeneous powder. This powder is mostlyapplied by the method known as the fluidized bed method. This method isessentially a dipping process wherein the article to be coated ispreheated to a temperature above the melting point of the coatingcomposition and then introduced into a fluidized mass of coatingcomposition powder articles.

Powdered thermosetting, curable coating compositions may be applied tothe substrate in the same way, requiring, however, two heat treatments,firstly the preheating of the object to be coated and subsequently thecuring treatment of the coated object. For this reason the electrostaticpowder spray application method has been developed, in which only oneheat treatment is required, namely the curing treatment, and this methodhas the additional advantage that thinner layers (less than 100 microns)may be applied than in the fluidized bed method. Due to the relativelyhigh viscosity of the molten powder, coatings are provided (even in onetreatment) which are substantially thicker than can be obtained by theconventional coating methods using solutions of the coating material.Sharp edges or bends are also much better coated by the powder coatingprocesses.

The formulation of fusible, powdered coating compositions forapplication by powder spray methods and fluidized bed processesintroduces requirements for film-forming materials which are entirelydifferent from those met in the formulation of conventional coatings. Itwill be clear that the film-forming material must be a solid which canreadily be converted into a free-flowing powder and is non-caking undernormal storage conditions, and that the material must be capable offusing at an elevated temperature below its degradation or decompositiontemperature.

In practice the manufacture of a thermoplastic powder coating hasinvolved much fewer difficulties than that of a thermosetting powdercoating. This is due to the fact that the thermoplastic powder coatingafter application hardens by simple cooling, whereas a thermosettingsystem has to undergo cross-linking to obtain the desired filmproperties. For this purpose it is necessary to introduce a curingagent, cross-linking agent or catalyst into the system, which involvesspecial problems.

Up till now the most important thermosetting powder coating systems areentirely based upon epoxy resins, which have as their main disadvantagepoor outdoor durability.

Hence there is still a need for powdered free-flowing, fusible,thermosetting coating compositions which are stable during storage,which can be used in electrostatic powder-spray coating processes, andwhich have a reduced epoxy resin content and therefore can be heat-curedin an acceptable time to a uniform coating having satisfactory chemicaland mechanical properties and an acceptable price.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide curablethermosetting coating compositions which are suitable for application bypowder spray methods and fluidized bed coating processes andparticularly to provide solid modified polyester resins to becross-linked by polyepoxide resins, which can be used in coating powdersto be applied by powder spray methods and fluidized bed coatingprocesses.

Another object of the present invention is to provide thermosettingresin compositions containing said solid, modified polyester resin andpolyepoxide resin in the form of stable, free-flowing powder suitablefor application in powder spray methods and fluidized bed coatingprocesses.

DESCRIPTION OF THE INVENTION

The present invention therefore provides a mixture of 4 to 25% andpreferably 8 to 15% by weight of polyepoxide resin with 75 to 96% andpreferably 85 to 92% of solid modified polyester resins having an acidnumber from 30 to 100, preferably from 40 to 80 and most preferably from55 to 70, and softening in the range of 60° C. to 130° C. (modified balland ring test) which can be cross-linked with the polyepoxide resin,said modified polyester resins comprising the reaction product of ananhydride of a polybasic, organic carboxylic acid and a polyester resin,having a hydroxyl number from 15 to 50, preferably from 15 to 40 andmost preferably from 25 to 40, of which the acid component comprises adibasic, aromatic carboxylic acid and of which the alcohol componentcomprises:

(a) from 0 to 100 mole% (based on the total) alcohol component of thepolyester) of an alcohol having the general formula: ##STR1## in whichR¹ and R² represent alkylene groups having from 2 to 4 and preferably 2to 3 carbon atoms, R represents a direct bond between the rings or analkylidene group having from 1 to 4, and preferably 3 or 4 carbon atoms,or a cycloalkylidene group having 6 carbon atoms, or a carbonyl group,or a sulphone group, x and y are numerals each being at least one, thesum of x and y being not greater than 6, and R⁴ and R⁵ represent ahydrogen atom or alkyl radical having from 1 to 6 carbon atoms;

(b) from 0 to 40 mole % (based on the total alcohol component of thepolyester) of a glycidyl ester having the general formula: ##STR2## inwhich R is a straight or branched chain, saturated or unsaturatedhydrocarbon radical having from 4 to 20 carbon atoms, or a substitutedor unsubstituted benzene nucleus; and

(c) from 0 to 100 mole % (based on the total alcohol component of thepolyester) of at least one dihydric, aliphatic alcohol, the sum of thealcohol components (a), (b) and (c) being 100 mole %.

As the anhydride of the polybasic organic carboxylic acid may be usedone or more anhydrides of aromatic, at least tribasic carboxylic acids,such as the anhydride of trimellitic acid, pyromellitic acid,hemimellitic acid, benzophenone tetracarboxylic acid, and naphthalenetetracarboxylic acid. Also a mixture of anhydride of at least tribasicaromatic carboxylic acid and up to 50 mole % (of the mixture ofanhydride) of one or more anhydrides of saturated or unsaturated,aliphatic, aromatic, cyclo-aliphatic or heterocyclic dibasic or highercarboxylic acid such as maleic acid, succinic acid, butanetetracarboxylic acid, tricarballylic acid, phthalic acid,tetrahydrophthalic acid, endomethylene tetrahydrophthalic acid,hexachloroendomethylene tetrahydrophthalic acid, tetrahydrofurantetracarboxylic acid, cyclopentane tetracarboxylic acid and maleopimaricacid, may be used.

If the polyester to be reacted with the anhydride of the polybasic,organic carboxylic acid has a high melting point on the order of about80° C. and over, and more preferably about 100° C. and over, from 0 to50 mole % and in fact from more than 50 to 100 mole% of the totalanhydride may be one or more anhydrides of saturated or unsaturated,aliphatic, aromatic, cyclo-aliphatic or heterocyclic dibasic and higherpolycarboxylic acids such as for example any of the acids mentioned inthe preceding paragraph. The powder coating composition obtained byforming a mixture of the resultant solid modified polyester withpolyepoxide resins exhibits improved rheological properties in themolten state accompanied by good (i.e., moderate to excellent) powderstability. However, the preferred powder coatings are obtained throughthe use of anhydrides of at least tribasic aromatic acids alone or inadmixture with anhydrides of dibasic or higher acids, the best resultsbeing obtained in most cases when substantially all of the anhydridecomponent is made up of at least tribasic aromatic acid anhydrides,including those having one, two and more anhydride groups.

As the dibasic, aromatic carboxylic acid in the acid component of thepolyester resin may be used: orthophthalic acid, terephthalic acid and,isophthalic acid, esters of these acids with lower aliphatic, monohydricalcohols such as methanol, or ethanol. The dibasic, aromatic acids maybe used either singly or in combination with one another. The preferreddibasic aromatic acid is terephthalic acid. It has in some cases beenfound advantageous to use up to 10 mole % (based on the total acidcomponent) of a polybasic, aliphatic carboxylic acid, such as adipicacid, hexachlorophthalic or tetrahydrophthalic acid, or of a tribasic,aromatic carboxylic acid, such as trimellitic acid or pyromellitic acid.

Examples of the diols forming component (a) of the polyester resininclude, 2,2'-di-(4-beta-hydroxyethoxyphenyl)-propane;2,2'-di-(4-beta-hydroxyethoxy-phenyl)-butane;2,2'di-(4-hydroxypropoxyphenyl)-propane;2,2'-di-(3-methyl-4-beta-hydroxyethoxyphenyl)-propane; thepolyoxyethylene or polyoxypropylene ether of 4,4¹ -isopropylidenediphenol, wherein both phenolic groups are oxyethylated and/oroxypropylated and the average number of oxyethylene and/or oxypropylenegroups is from 2 to 6; di-(4-beta-hydroxyethoxyphenyl)-ketone anddi-(4-beta-hydroxypropoxyphenyl)-ketone.

The preferred diols are 2,2'-di-(4-beta-hydroxyethoxyphenyl)-propane and2,2'-di-(4-hydroxypropoxyphenyl)-propane.

The alcohol component (b) of the polyester resin comprises glycidlyesters and those that can be used include, lauric acid glycidyl ester,benzoic acid glycidyl ester and glycidyl esters of saturated aliphaticmonocarboxylic acids having tertiary or quanternary carbon atoms inalpha-position relative to the carboxyl groups (available under thetrade name of "Versatic acids"). The latter glycidyl esters arepreferred.

The alcohol, component (c) of the polyester resin comprises dihydricaliphatic alcohols such as 2,2-dimethylpropanediol-1,3, propyleneglycol-1,2 1,4-cyclohexanedimethanol and ethylene glycol, which alcoholsmay contain other functional groups than hydroxyl groups, such as e.g.diethylene glycol. The dihydric aliphatic alcohols may be used eithersingly or in combination with one another.

It has in some instances been found advantageous to use up to 10 mole %(based on the total alcohol component) of aliphatic trihydric orpolyhydric alcohols, such as trimethylol propane and pentaerythritol. Inall cases, however, the sum of the alcohol components (a), (b), (c) and,optionally, the aliphatic trihydric or polyhydric alcohol is 100 mole %.

The polyester resins are prepared by the general techniques employed inthe preparation of polyester resins. They can be conveniently made byheating all the reactants, while stirring, up to a temperature of 250°C., while an inert gas (e.g. nitrogen) is continuously passed throughthe reaction mixture to remove the water formed during theesterification reaction or the lower alcohol in re-esterificationreactions. At the end of the esterification reaction, a vacuum of about100 mm Hg is applied and some glycol is distilled off.

The anhydride of the polybasic, organic carboxylic acid is added to thepolyester, while the latter is in molten form, and the mixture is heatedfor about 1-15 hrs., preferably 1-3 hrs., at about 180°-250° C.,preferably 180°-210° C. The reaction product is then cooled to about140° C. and poured into shallow receptacles to solidify. After cooling,the reaction product is crushed into small pieces and ground, suitablyin a pin disc mill, to a free-flowing powder having the desired particlesize range (approximately 20-150 microns). The free-flowing powder thusobtained may be subjected to a screening treatment to adjust the desiredaverage particle size to the specific type of application for which thepowder will be used.

As will be noted from the examples given below, the softening point ofboth the polyester to be reacted with the anhydride of a polybasic,organic carboxylic acid and the solid, modified polyester obtained ispreferably from 60° C. to 130° C., but in some instances the softeningpoint of the polyester to be modified may be lower, so that afterreaction with the anhydride of a polybasic, organic carboxylic acid, thesoftening point of the modified polyester is from 60° C. to 130° C.

The polyepoxide resins used cross-linking agent for the solid, modifiedpolyester resin are essentially solid (at 25° C.) compounds or mixturesof compounds, the molecules of which contain an average number of atleast two epoxy groups.

Preferably the average number of epoxy groups contained in the moleculeof the polyepoxide resin is three or more. Particularly desirable forthe purpose of the invention is triglycidyl isocayanurate, althoughvarious other well-known polyepoxide resins may be used, provided thatthey contain at least two epoxy groups in their average molecule andthat in combination with the solid modified polyester resins they leadto thermosetting coating compositions having a good powder stability ashereafter defined. Polylepoxide resins meeting the foregoing criteriamay be found for example in U.S. Pat. 260/835 3,397,254 to J. Wynstra etal.

In preparing the stable, powdered free-flowing resin compositionsaccording to the present invention, 75 to 96% by weight, preferably 85to 92% by weight of the powdered modified polyester resin is mixed with4 to 25% by weight, preferably 8 to 15% by weight of polyepoxide resinhaving at least two epoxy groups. The foregoing weight percentages arebased on the weight of the total composition.

The solid modified polyester resin and the polyepoxide resin are mixed,for example in an extruder, for a time and at a temperature (at or abovetheir melting points) such that they remain substantially unreacted, arethen cooled to solidify the substantially unreacted mixture, and aresubsequently crushed and ground in a suitable grinding device such as apin disc mill, to a free-flowing powder having a particle size range ofapproximately 20-150 microns. The free-flowing powder so obtained may besubjected to a screening treatment to adjust the desired averageparticle size to the specific type of application for which the powderwill be used. Substantial reaction between the solid modified polyesterresin and the polyepoxide resin is accompanied by a noticeableimpairment in the flow characteristics of the powder coatingcompositions in the molten state. However, it is an advantage of thepresent invention that reaction between the solid modified polyesterresin and the polyepoxide resin in the extruder is not normally aproblem and hence good control over product composition can bemaintained during large scale production.

When filler and pigment components are employed, an alternativeprocedure is to melt the polyepoxide resin, add the filler and pigmentcomponents with mixing in an extruder, cool the blend obtained tosolidify it and subsequently crush and grind it to a free-flowing powderhaving the required particle size range, which is then mixed with thesolid, powered modified polyester resin having the same requiredparticle size range.

The homogeneous, pulverulent coating compositions may also includevarious well-known functional modifiers such as grinding aids, curingagents or accelerators, flow control agents, surface-active agents,heat-stable organic or inorganic pigments, inert fillers, inhibitors,abrasives and plasticizers in their usual effective proportions.

After application of the coating compositions to the substrate, thecoatings are cured at a temperature from about 120° C. to about 250° C.for a period of up to about 60 minutes. The curing treatment ispreferably carried out for 10 to 40 minutes at 150° C. to 200° C.

The invention provides certain advantages in the matter of cure time, inthat at a given temperature one may use the composition and method ofthe invention in such a way as to obtain shorter cure cycles than arenormally experienced with other systems, now in use, which are basedprimarily on polyester resins.

The invention will be further illustrated by the following examples. Inall examples concerning preparation of the final coating composition,modified polyester, epoxy resin and titanium dioxide pigment (in aweight ratio of 1:2, pigment to binding medium) were thoroughly drymixed and then passed through an extruder in which they were melted andmixed, with a residence time of about 30 to 45 seconds, and thenpromptly discharged, cooled and powdered. In all examples and in theappended claims all softening points of the polyester and modifiedpolyester resins were determined by a modified version of the ball andring method according to A.S.T.M. Specification No. E 28-58 T. Themethod is modified in that the first temperature recorded is thetemperature at which the ball begins to move and the last temperature isthe temperature at which the ball strikes the bottom plate. In view ofthe application as powder coating, it has been found advantageous forthe adjustment of the characteristics of the polyester resin to bemodified to use these figures, rather than those set out in the A.S.T.M.Specification mentioned above.

EXAMPLE I

Into a suitable reaction vessel equipped with thermometer, stirrer,separating column and inert gas inlet tube, were introduced 2816 g (9 gmol) of the diether of ethylene glycol and bisphenol A, 480 g (2 g mol)of Cardura E (Trade Mark; glycidyl ester of branched chainmonocarboxylic acids having from 9 to 11 carbon atoms), and 1660 g (10 gmol) of terephthalic acid. The contents of the vessel were heated to atemperature of about 180 to 250° C. and held at that temperature whilestirring, whereby the water of the esterification reaction was removedfrom the reaction mass by bubbling nitrogen gas through it. The heatingwas continued until an acid number of 7 was reached. The resultantpolyester has a softening point of 78-96° C. and a hydroxyl number of30. 1000 g of this polyester resin were heated in a reaction vessel ofthe same type as described above to 200°-210° C. while nitrogen wasbubbled through the molten mass. Then 103 g (0.53 g mol) of theanhydride of trimellitic acid were added with stirring, whereafter theresultant mixture obtained was heated for 3 hours at 200°-210° C., untilan acid number of about 62 to 63 was obtained. The heating was stopped,the resultant product was cooled and solidified. The resultant modifiedpolyester resin had an acid value of 62.8, a hydroxyl value of 0 and asoftening point of 99°-111.5° C. The product is identified below as"Acid A".

EXAMPLES II and III

In the same apparatus as described in Example I, two other polyesterresins were prepared, using the ingredients given in Table I. The acidnumbers (AN), hydroxyl numbers (HN) and softening points (SP) in ° C. ofthese polyester resins are also indicated in Table I.

                  TABLE I                                                         ______________________________________                                                       Moles                                                          Ex-            Al-                                                            am-            co-           Moles                                            ple  Alcohol   hol     Acid  Acid  AN   HN   SP                               ______________________________________                                        (II) Neopentyl-                                                                              9       TPA.sup.2                                                                           10    8    25   95-                                   glycol                                  110° C.                        DEGBA.sup.1                                                                             0.66                                                                Cardura E 1.57                                                           (III)                                                                              Neopentyl-                                                                              3       TPA.sup.2                                                                           10    8.5  32   74-                                   glycol                                  88° C.                         Ethylene  5                                                                   glycol                                                                        Hexane-   1                                                                   diol-1,6                                                                      Cardura E 2                                                              ______________________________________                                         .sup.1 DEGBA = diether of ethylene glycol and bisphenol A                     .sup.2 TPA = terephthalic acid                                           

Modified Polyester Resins

(IIa) 1000 g of the polyester resin of Example II were heated in thesame apparatus and in the same way as described in Example I with 86.0 g(0.45 g mol) of the anhydride of trimellitic acid, whereby a modifiedpolyester resin, hereafter identified as "Acid B" was obtained, havingan acid number of 51, a hydroxyl number of 5 and a softening point of96.6°-114° C.

(IIIa) 1250 g of the polyester resin of Example 3 were heated in thesame apparatus and in the same way as in Example I with 141.3 g (0.74 gmol) of the anhydride of trimellitic acid, whereby a modified polyesterresin, hereafter identified as "Acid C," was obtained, having an acidnumber of 69, a hydroxyl number of 0 and a softening point of 82°-99.5°C.

EXAMPLE IV

With the acid of "Acid A" a coating composition was prepared by mixing80 g of powdered "Acid A"; 15 g of a powdered polyglycidylether oforthocresol-formaldehyde novolak, having an epoxy equivalent weight* of225 and a melting point of 73° C. (Durran's mercury method as describedby Gardner and Sward in "Paint Testing Manual," 12th edition, 1962 p.367); and 0.3% by weight based on "Acid A" oftris-(2,4,6-dimethylaminomethyl)-phenol, a hardening catalyst, soldunder the commercial indication "DMP-30" by Rohm and Haas Chemical Corp.of this composition 80-90% had a particle size between 70 and 100microns. The pulverulent, pigmented resin mixture was applied on 1 mmthick mild steel panels by the electrostatic spray-coating method, insuch a way that on subsequent curing at 180° C. for 30 minutes a uniformcoating having a thickness of about 80 microns was obtained.

EXAMPLE V

A coating composition was prepared by mixing 88 g of powdered "Acid A"and 12 g of powdered triglycidyl isocyanurate, having an epoxyequivalent weight of 102 and a melting point of 95°-115° C. (ring andball method). Of this composition 80-90% had a particle size between 70and 100 microns. The powdered, free-flowing, pigmented resin mixture wasapplied on 1 mm thick mild steel panels by the electrostaticspray-coating method, in such a way that on subsequent curing at 180° C.for 30 minutes a uniform coating having a thickness of about 40 micronswas obtained.

EXAMPLE IV

A coating composition was prepared by mixing 90 g of powdered "Acid B"and 10 g of the powdered triglycidyl isocyanurate metioned in Example V.Of this composition 80-90% had a particle size between 70 and 100microns. The powdered, free-flowing pigmented resin mixture was appliedon 1 mm thick mild steel panels by the electrostatic spray-coatingmethod, in such a way that on subsequent curing at 150° C. for 30minutes a uniform coating having a thickness of about 70 microns wasobtained.

EXAMPLE VII

A coating composition was prepared by mixing 88 g of powdered "Acid C"and 12 g of the powdered triglycidyl isocyanurate of Example V, of thiscomposition 80-90% had a particle size between 70 and 100 microns. Thepowdered, free-flowing, pigmented resin mixture was applied on 1 mmthick mild steel panels by the electrostatic spray-coating method, suchthat on subsequent curing at 150° C. for 30 minutes a uniform coatinghaving a thickness of about 70 microns was obtained.

The resin compositions of the Examples IV-VIII and the coated mild steelpanels obtained in these Examples were then investigated as to theirpowder stability and mechanical properties, respectively. The "powderstability" as indicated throughout this application and in the appendedclaims was determined as follows:

50 g of the pigmented, powdered, free-flowing composition (of which80-90% had a particle size between 70 and 100μ) was heated in a glassbeaker at 40° C. for 7 days. If the resin particles were not sinteredtogether and the powder was still completely free-flowing, the powderstability was rated as excellent (E). If in the powder only someparticles were sintered together, forming soft lumps, the powderstability was rated as moderate (M); if all particles were sinteredtogether, the powder stability was rated as bad (B).

The "flexibility" was determined on the basis of the specimens of 1 mmthick mild steel panels, upon which an amount of the pulverulent resinmixture was applied by the electrostatic spray-coating method, and whichwere subsequently cured. Flexibility was rated as passing (P) or failing(F), depending upon whether or not the steel panel with the coatingcould be bent 180° over a 3/4 inch diameter mandrel without impairingthe coating. If the film cracked or broke, it was rated as failing. The"shock resistance" was determimed with the "Erichsen Schlagprufgerat"according to German specification DIN 53,156 with the same specimensused for the flexibility test. The "hardness" was determined as"Pendelharte nach Konig" according to German specification DIN 53,157with the same specimens used for the flexibility test. The results aresummarized in Table II below.

                  TABLE II                                                        ______________________________________                                         Example       IV       V        VI     VII                                   ______________________________________                                        Powder stability                                                                             E        E        E      M                                     Flexibility    P        P        P      P                                     Shock resistance (mm)                                                                        2-3      4-5       2     3-4                                   Hardness (sec.)                                                                              183      195      210    180                                   ______________________________________                                    

EXAMPLES VIII and IX

In the same apparatus as described in Example I two other polyesterresins were prepared using the ingredients as summarized in Table III.The same abbreviations are used as in Table I.

                  TABLE III                                                       ______________________________________                                                        Moles                                                         Ex-             Al-                                                           am-             co-          Moles                                            ple  Alcohol    hol     Acid acid  AN   HN   SP                               ______________________________________                                        VIII Propylene  9       TPA  10    9.2  28   96-                                   glycol                                  113° C.                        Dipropylene                                                                              2                                                                  glycol                                                                   IX   Neopentyl- 3       TPA  10    6.4  36.5 80-                                   glycol                                  92° C.                         Ethylene   6                                                                  glycol                                                                        Diethylene 1                                                                  glycol                                                                        Cardura E  1                                                             ______________________________________                                    

Modified Polyester Resins

(VIIIa) 1000 g of the polyester resin of Example VIII were heated in thesame apparatus and in the same way as described in Example I with 97 g(0.5 g mole) of trimellitic acid anhydride, whereby a modified polyesterresin, hereafter indicated as "Acid D" was obtained, having an acidnumber of 57 and a softening point of 108°-120° C.

(IXa) 1000 g of the polyester resin of Example IX were heated in thesame apparatus and in the same way as described in Example I with 126 g(0.65 g mole) of trimellitic acid anhydride, whereby a modifiedpolyester resin, hereafter indicated as "Acid E" was obtained, having anacid number of 66 and a softening point of 94°-104° C.

Final Coating Compositions

(VIIIb) With aid of the "Acid D" a coating composition was prepared bymixing 100 g of powdered "Acid D," and 11.1 g of the powderedtriglycidyl isocyanurate, mentioned in Example V. Of this compositionmore than 90% had a particle size from 70 to 100 microns. The powdered,free-flowing, pigmented resin mixture was applied on 1 mm thick mildsteel panels by the electrostatic spray-coating method in such a waythat on subsequent curing at 200° C. for 10 minutes a uniform coatinghaving a thickness of about 70 to 80 microns was obtained. The powderstability and the mechanical properties found were as follows:

Powder stability: E

Flexibility: P

Shock resistance: 2 mm

Hardness: 192 sec

(IXb) With the aid of "Acid E" a coating composition was prepared bymixing 645 g of powdered "Acid E" and 105 g of the powdered triglycidylisocyanurate mentioned in Example V. Of this composition more than 90%had a particle size from 70 to 100 microns. The powdered, free-flowing,pigmented resin mixture was applied on 1 mm thick mild steel panels bythe electrostatic spray-coating method in such a way that on subsequentcuring at 200° C. for 10 minutes a uniform coating having a thickness ofabout 70 to 80 microns was obtained. The powder stability and themechanical properties of the coating were determined to be as follows:

Powder stability: M

Flexibility: P

Shock resistance: 2-3 mm

Hardness: 197 sec.

EXAMPLE X

In the same apparatus as described in Example I a polyester resin wasprepared from 9 moles of neopentylglycol, 1 mole of 1,6-hexanediol, 1mole of Cardura E and 10 moles of terephthalic acid. The polyesterobtained had an acid number of 8.3, a hydroxyl number of 38.3 and asoftening point of 86°-103° C. 750 g of this polyester were heated inthe same apparatus and in the same way as described in Example I with amixture of 49.0 g of trimellitic acid anhydride and 102.0 g ofmaleopimaric acid anhydride, whereby a modified polyester resin,hereafter indicated as "Acid F" was obtained, having an acid number of65.6 and a softening point of 92°-108° C. With the aid of the "Acid F" acoating composition was prepared by mixing 860 g of powdered "Acid F"and 140 g of the powdered triglycidyl isocyanurate as described inExample V. Of this composition more than 90% had a particle size from 70to 100 microns. The powdered, free-flowing, pigmented resin mixture wasapplied on 1 mm thick mild steel panels by the electrostaticspray-coating method in such a way that on subsequent curing at 200° C.for 10 minutes a uniform coating having a thickness of about 50 to 60microns was obtained. The powder stability and the mechanical propertiesof the coating were determined to be as follows:

Powder stability: E

Flexibility: P

Shock resistance: 3-4 mm

Hardness: 197 sec.

EXAMPLE XI

In the same apparatus as described in Example I, a polyester resin wasprepared from 5 moles of ethylene glycol, 3 moles of neopentylglycol, 1mole of 1,4-cyclohexanedimethanol, 2 moles Cardura E and 10 moles ofterephthalic acid. The resultant polyester had an acid number of 9.3, ahydroxyl number of 32.5 and a softening point of 74°-83° C. 1824 g ofthis polyester were heated in the same apparatus and in the same way asdescribed in Example I with 218.9 g of trimellitic acid anhydride,whereby a modified polyester resin, hereafter identified as "Acid G" wasobtained, having an acid number of 66 and a softening point of96°-117.5° C. With aid of the "Acid G" a coating composition wasprepared by mixing 580 g of powdered "Acid G," and 170 g of powdereddiglycidyl terephthalate. Of this composition more than 90% had aparticle size from 70 to 100 microns. The powdered, free-flowing,pigmented resin mixture was applied on 1 mm thick mild steel panels bythe electrostatic spray-coating method in such a way that on subsequentcuring at 200° C. for 20 minutes a uniform coating having a thickness ofabout 50 to 60 microns was obtained. The powder stability and themechanical properties of the coating were determined to be as follows:

Powder stability: M

Flexibility: P

Shock resistance: 1 mm

Hardness: 197 sec.

EXAMPLE XII

In the same apparatus as described in Example I, a polyester resin wasprepared from 6 moles of ethylene glycol, 3 moles of neopentylglycol, 1mole of diethylene glycol, 1 mole of Cardura E and 10 moles ofterephthalic acid. The resultant polyester had an acid number of 6.4, ahydroxyl number of 36.5 and a softening point of 81°-97° C. 750 g ofthis polyester were heated in the same apparatus and in the same way asdescribed in Example I with 93.9g of trimellitic acid anhydride, wherebya modified polyester resin, hereafter identified as "Acid H" wasobtained, having an acid number of 83.3 and a softening point of94°-104° C. With aid of "Acid H" a coating composition was prepared bymixing 600 g of powdered "Acid H" and 66 g of powdered triglycidylisocyanurate. Of this composition more than 90% had a particle size from70 to 100 microns. The powdered, free-flowing, pigmented resin mixturewas applied on 1 mm thick mild steel panels by the electrostaticspray-coating method in such a way that on subsequent curing at 200° C.for 10 minutes a uniform coating having a thickness of about 50 to 60microns was obtained. The powder stability and the mechanical propertiesof the coating were determined to be as follows:

Powder Stability: E

Flexibility: P

Shock resistance: 2-3 mm

Hardness: 200 sec.

EXAMPLES XIII-XV

In the same apparatus as described in Example I three other polyesterresins were prepared, using the ingredients set forth in Table IV. Thesame abbreviations are used as in Table I.

                  TABLE IV                                                        ______________________________________                                                       Moles                                                          Ex-            Al-                                                            am-            co-           Moles                                            ple  Alcohol   hol     Acid  Acid  AN   HN   SP                               ______________________________________                                        XIII Neopentyl-                                                                              3       TPA   10    5.5  33.7 86-                                   glycol                                  102° C.                        Ethylene- 6                                                                   glycol                                                                        2,2,4-Tri-                                                                              2                                                                   methyl-                                                                       hexanediol-                                                                   1,6                                                                      XIV  DEGBA     3.5     TPA   10    5.9  49   64-                                                                           84° C.                         Cardura E 3                                                                   1,4-Cyclo-                                                                              4.5                                                                 hexanedi-                                                                     methanol                                                                 XV   Ethylene  5       TPA   10    6.7  19   84.5-                                 glycol                                  105° C.                        Cardura E 2                                                                   Neopentyl-                                                                              3                                                                   glycol                                                                        Hexane-   1                                                                   diol-1,6                                                                 ______________________________________                                    

Modified polyester resins

XIIIa 1000 g of the polyester resin of Example XIII were heated in thesame apparatus and in the same way as described in Example IX with amixture of 58.5 g of trimellitic acid anhydride and 30.5 g of succinicacid anhydride, whereby a modified polyester resin hereafter identifiedas "Acid K" was obtained, having an acid number of 50.1 and a softeningpoint of 93°114° C.

XIVa 750 g of the polyester of Example XIV were heated in the sameapparatus and in the same way as described in Example I with a mixtureof 126 g of trimellitic acid anhydride and 4 g of maleic acid anhydride,whereby a modified polyester resin, hereafter identified as "Acid L" wasobtained, having an acid number of 94 and a softening point of 112°-126°C.

XVa 750 g of the polyester resin of Example XV were heated in the sameapparatus and in the same way as described in Example I with a mixtureof 41 g of trimellitic acid anhydride and 14 g of maleic acid anhydride,whereby a modified polyester resin hereafter identified as "Acid M" wasobtained, having an acid number of 36 and a softening point of 87°-115°C.

Final Coating Compositions

(XIIIb) With aid if Acid K a coating composition was prepared by mixing440 g of powdered Acid K and 60 g of the powdered triglycidylisocyanurate, mentioned in Example V. Of this composition more than 90%had a particle size from 70 to 100 microns. The powdered, free-flowingpigmented resin mixture was applied on 1 mm thick mild steel panels bythe electrostatic spray-coating method in such a way that on subsequentcuring at 200° C. for 10 minutes a uniform coating having a thickness ofabout 50 to 60 microns was obtained. The powder stability and themechanical properties are given in Table V.

(XIVb) With aid of Acid L a coating composition was prepared by mixing625 g of powdered Acid L and 75 g of the powdered triglycidylisocyanurate, mentioned in Example V. Of this composition more than 90%had a particle size from 70 to 100 microns. The powdered free-flowingpigmented resin mixture was applied on 1 mm thick mild steel panels bythe electrostatic spray-coating method in such a way that on subsequentcuring at 200° C for 10 minutes a uniform coating having a thickness ofabout 60 to 70 microns was obtained. The powder stability and themechanical properties are given in Table V.

(XVb) With aid of Acid M a coating composition was prepared by mixing630 g of powdered Acid M and 120 g of the powdered triglycidylisocyanurate, mentioned in Example V. Of this composition more than 90%had a particle size from 70 to 100 microns. The powdered free-flowingpigmented resin mixture was applied on 1 mm thick mild steel panels bythe electrostatic spray-coating method in such a way that on subsequentcuring at 200° C. for 10 minutes a uniform coating having a thickness ofabout 50 to 60 microns was obtained. The powder stability and themechanical properties are given in Table V.

                  TABLE V                                                         ______________________________________                                         Example          XIII     XIV      XV                                        ______________________________________                                        Powder stability  E        E        M                                         Flexibility       P        P        P                                         Shock resistance (mm)                                                                            6        1        1                                        Hardness (sec.)   192      180      200                                       ______________________________________                                    

EXAMPLE XVI

In the same apparatus as described in Example I, a polyester resin wasprepared from 11 moles of neopentyl glycol and 11 moles oftetrahydrophthalic acid. The resultant polyester had an acid number of7.5, a hydroxyl number of 40 and a softening point of 56°-63° C.

1000 g of this polyester resin were heated in the same apparatus and inthe same way described in Example I with 257.9 g of hexachlorophthalicacid anhydride, whereby a modified polyester resin, hereinafteridentified as "Acid N" was obtained, having an acid number of 34 and asoftening point of 74°-78° C.

With the aid of "Acid N" a coating composition was prepared by mixing660 g of powdered "Acid N" and 90 g of powdered triglycidylisocyanurate. Of this composition more than 90% had a particle size offrom 70 to 100 microns.

The powdered, free-flowing, pigmented resin mixture was applied on 1 mmthick mild steel panels by the electrostatic spray-coating method insuch a way that on subsequent curing at 200° C. for 10 minutes a uniformcoating having a thickness of about 50 to 60 microns was obtained.

The powder stability and the mechanical properties of the coating weredetermined to be as follows:

Powder stability: E

Flexibility: P

Shock resistance: 3-3.

EXAMPLE XVII

In the same apparatus as described in Example I, a polyester resin wasprepared from 6 moles of neopentyl glycol, 6 moles of1,4-cyclohexanedimethanol and 10 moles of terephthalic acid. Theresultant polyester had an acid number of 7.4, a hydroxyl number of 55and a softening point of 118°-125° C.

1000 g of the polyester were heated in the same apparatus and in thesame way described in Example I with 149.2 of tetrahydrophthalic acidanhydride, whereby a modified polyester resin, hereinafter identified as"Acid P," was obtained, having an acid number of 46 and a softeningpoint of 68°-75° C. with the aid of "Acid P" a coating composition wasprepared by mixing 675 g of powdered "Acid P" and 75 g of powderedtriglycidyl isocyanurate. Of this composition more than 90% had aparticle size of from 70 to 100 microns.

The powdered, free-flowing, pigmented resin mixture was applied on 1 mmthick mild steel panels by the electrostatic spray-coating method insuch a way that on subsequent curing at 200° C. for 10 minutes a uniformcoating having a thickness of about 50 to 60 microns was obtained.

The powder stability and the mechanical properties of the coating weredetermined to be as follows:

Powder stability: E

Flexibility: P

Shock resistance 4-5

What is claimed is:
 1. A homogeneous pulverulent substantially unreactedthermosettable composition comprising a mixture of:(1) 4% to 25% byweight of a polyepoxide compound or mixture of compounds, the moleculesof which contain an average of at least two epoxy groups, and (2) 75.%to 96% by weight of a solid modified polyester resin having an acidnumber of from 30 to 100, and which softens in the range 60° C. to 130°C., said solid modified polyester resin comprising the reaction productof:(a) an anhydride of a polybasic, organic carboxylic acid, and (b) apolyester resin having a hydroxyl number of from 15 to 50, the acidcomponent of this polyester resin comprising a dibasic, aromaticcarboxylic acid and the alcohol component comprising: (c) from 0 to 100mole % (based on the total alcohol component of the polyester) of analcohol having the general formula: ##STR3## in which R¹ and R²represent alkylene groups having from 2 to 4 carbon atoms, R³ representsa direct bond between the rings or an alkylidene group having from 1 to4 carbon atoms or a cycloalkylidene group having 6 carbon atoms, or acarbonyl group, or a sulphone group, x and y are numerals each being atleast one, the sum of x and y being not greater than 6, and R⁴ and R⁵represent a hydrogen atom or alkyl radical having from 1 to 6 carbonatoms; (d) from 0 to 40 mole % (based on the total alcohol component ofthe polyester) of a glycidyl ester of the general formula: ##STR4## inwhich R is a straight or branched chain, saturated or unsaturatedhydrocarbon radical having from 4 to 20 carbon atoms, or a substitutedor unsubstituted benzene nucleus, and (e) from 0 to 100 mole % (based onthe total alcohol component of the polyester) of at least one dihydric,aliphatic alcohol,the sum of the alcohol components (c), (d), and (e)being 100 mole %, and said composition having a good powder stability.2. A composition according to claim 1, in which (a) is an anhydride ofan aromatic at least tribasic carboxylic acid.
 3. A compositionaccording to claim 1, in which (a) is a mixture of an anhydride of anaromatic, at least tribasic carboxylic acid and up to 50 mole% (based onthe mixture of acid anhydrides) of an anhydride of a saturated orunsaturated, aliphatic or aromatic or cycloaliphatic dibasic carboxylicacid.
 4. A composition according to claim 1, wherein said polyesterresin (b) has a softening point of at least 80° C., and in whichanhydride (a) is composed of 0-100 mole % (based on the mixture of saidanhydrides) of one or more anhydrides of saturated or unsaturatedaliphatic or cycloaliphatic or heterocyclic polycarboxylic acids.
 5. Acomposition accoring to claim 1, in which the polyepoxide compound istriglycidyl isocyanurate.
 6. The composition of claim 1 being in powderform.
 7. The composition of claim 1 being a powder having a particlesize of about 20-150 microns.
 8. The composition of claim 1, whereinsaid polyester having a hydroxyl number of from 15 to 50 softens in therange of 60° C. to 130° C.
 9. A homogeneous pulverulent substantiallyunreacted thermosettable composition comprising a mixture of:(1) 4% to25% by weight of a polyepoxide compound or mixture of compounds, themolecules of which contain an average of at least two epoxy groups, and(2) 75% to 96% by weight of a solid modified polyester resin having anacid number of from 40 to 80, and which softens in the range 60° C. to130° C., said solid modified polyester resin comprising the reactionproduct of:(a) an anhydride of a polybasic, organic carboxylic acid, and(b) a polyester resin having a hydroxyl number of from 15 to 40, theacid component of this polyester resin comprising a dibasic, aromaticcarboxylic acid and the alcohol component comprising: (c) from 0 to 100mole % (based on the total alcohol component of the polyester) of analcohol having the general formula: ##STR5## in which R¹ and R²represent alkylene groups having from 2 to 4 carbon atoms, R³ representsa direct bond between the rings or an alkylidene group having from 1 to4 carbon atoms or a cycloalkylidene group having 6 carbon atoms, or acarbonyl group, or a sulphone group, x and y are numerals each being atleast one, the sum of x and y being not greater than 6, and R⁴ and R⁵represent a hydrogen atom or alkyl radical having from 1 to 6 carbonatoms; (d) from 0 to 40 mole % (based on the total alcohol component ofthe polyester) of a glycidyl ester of the general formula: ##STR6## inwhich R is a straight or branched chain, saturated or unsaturatedhydrocarbon radical having from 4 to 20 carbon atoms, or a substitutedor unsubstituted benzene nucleus, and (e) from 0 to 100 mole % (based onthe total alcohol component of the polyester) of at least one dihydric,aliphatic alcohol,the sum of the alcohol components (c), (d), and (e)being 100 mole %, and said composition having a good powder stability.10. A composition according to claim 9, in which (2) has an acid numberof from 55 to
 70. 11. A composition according to claim 9, in which (b)has a hydroxyl number of at least
 25. 12. A composition according toclaim 9, in which the polyepoxide compound is triglycidyl isocyanurate.13. The composition of claim 9, being in powder form.
 14. Thecomposition of claim 9, being a powder having a particle size of about20-150 microns.
 15. The composition of claim 9 wherein said polyesterhaving a hydroxyl number of from 15 to 50 softens in the range of 60° C.to 130° C.
 16. A homogeneous pulverulent substantially unreactedthermosettable composition comprising a mixture of:(1) 8% to 15% byweight of a polyepoxide compound or mixture of compounds, the moleculesof which contain an average of at least two epoxy groups, and (2) 85% to92% by weight of a solid modified polyester resin having an acid numberof from 40 to 80, and which softens in the range 60° to 130° C., saidsolid modified polyester resin comprising the reaction product of:(a) ananhydride of a polybasic, organic carboxylic acid, and (b) a polyesterresin having a hydroxyl number of from 15 to 40, the acid component ofthis polyester resin comprising a dibasic, aromatic carboxylic acid andthe alcohol component is: (c) from 0 to 100 mole % (based on the totalalcohol component of the polyester) of an alcohol having the generalformula: ##STR7## in which R¹ and R² represent alkylene groups having 2or 3 carbon atoms, R³ represents an alkylidene group having 3 or 4carbon atoms, x and y are numerals each being at least one, the sum of xand y being not greater than 6 and R⁴ and R⁵ represent hydrogen atoms,so that the two nuclei are benzene nuclei, (d) from 0 to 40 mole %(based on the total alcohol component of the polyester) of a glycidylester of the general formula: ##STR8## in which R is a branched chain,saturated alkyl group having from 4 to 10 carbon atoms, and (e) from 0to 100 mole % (based on the total alcohol component of the polyester) ofat least one dihydric, aliphatic alcohol, (f) from 0 to 10 mole % (basedon the total alcohol component of the polyester) of at least onealiphatic, at least trihydric alcohol,the sum of the alcohol components(c), (d), (e), and (f) being 100 mole %, and said composition having agood powder stability.
 17. A composition according to claim 16, in whichthe anhydride (a) is a mixture of an anhydride of an aromatic, at leasttribasic carboxylic acid and up to 50 mole % (based on the mixture ofacid anhydrides) of an anhydride of a saturated or unsaturated,aliphatic or aromatic or cycloaliphatic dibasic carboxylic acid.
 18. Acomposition according to claim 16, in which in the alcohol component (c)is from 0 to 10 mole%, (d) is from 0 to 20 mole% and (e) is from 75 to100 mole%.
 19. A composition according to claim 16, in which thepolyepoxide compound is triglycidyl isocyanurate.
 20. A compositionaccording to claim 16, in which the molecule of the polyepoxide resincontains an average of at least three epoxy groups and in which theanhydride (a) is trimellitic acid anhydride, pyromellitic acid anhydrideor hemimellitic acid anhydride.
 21. The composition of claim 16 being inpowder form.
 22. The composition of claim 16 being a powder having aparticle size of about 20-150 microns.
 23. The composition of claim 16wherein said polyester having a hydroxyl number of from 15 to 50 softensin the range of 60° C. to 130° C.
 24. The composition of claim 1,wherein said polyester includes up to 10 mole % (based on the totalalcohol component) of aliphatic trihydric or polyhydric alcohols. 25.The composition of claim 1 wherein said polyester includes up to 10 mole% (based on the total acid component) of a polybasic, aliphaticcarboxylic acid or of a tribasic, aromatic carboxylic acid.
 26. Thecomposition of claim 1 wherein said epoxide is polyglycidylether oforthocresol-formaldehyde novolak.
 27. The composition of claim 1 whereinsaid epoxide is diglycidyl terephthalate.
 28. The composition of claim 1wherein said polyester melts above about 100° C. and wherein saidanhydride includes at least one anhydride of saturated or unsaturated,aliphatic, aromatic, cycloaliphatic or heterocyclic dibasic and higherpolycarboxylic acids.